The present invention relates to a balloon catheter useful in medical dilatation procedures.
Angioplasty has gained wide acceptance in recent years as an efficient and an effective method for treating types of vascular diseases. In particular, angioplasty is widely used for opening stenoses in coronary arteries as well as for treating stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, a physician guides the catheter through the vascular system until the balloon is positioned across the stenoses. The balloon is then inflated by supplying liquid under pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of a blood vessel and pressing of the lesion into the blood vessel wall to reestablish acceptable blood flow through the blood vessel.
In order to treat very tight stenoses with small openings, there has been a continuing effort to reduce the profile of the catheter so that the catheter can reach and pass through the small opening of the stenoses. There has also been an effort to reduce the profile of the catheter after an initial use and deflation of the balloon to permit passage of the catheter through additional lesions that are to be treated or to allow entry and retreatment of lesions that reclose after initial treatment. It is also desired that the balloon component of the catheter deflate from an inflated mode to a predictable and reduced profile so that the balloon catheter can be withdrawn from a blood vessel without becoming caught.
Reducing a catheter profile requires a consideration of two deflated balloon profiles. The initial profile is that of the unused catheter before it is inserted into a blood vessel for the first time. This profile may be controlled by the wrap given to the deflated balloon by the manufacturer or the surgeon. The second deflated balloon profile is that obtained after the catheter has been used and the catheter balloon has been inflated and deflated within the body. The second profile is rarely, if ever, as compact as the first deflated profile and, with many balloon materials often takes an entirely different appearance.
One factor manipulated to reduce the profile of the dilatation catheter is the wall thickness of the balloon material. Balloons for dilatation balloon catheters have been made from a wide variety of polymeric materials. Typically the balloon wall thicknesses have been on the order of 0.0004 to 0.003 inches for most materials. There have been continuing efforts, however, to develop ever thinner walled balloon materials, while still retaining the necessary distensibility and burst pressure rating, so as to permit lower deflated profiles.
Another factor manipulated to reduce the profile of the catheter is the conformation of the balloon which is altered so that the balloon acquires a low profile shape when the balloon is deflated. Typically, oriented PET balloons (a very common catheter balloon material) forms a pair of opposed radially extending flat wings when subjected to a negative pressure. This winged configuration can easily be wrapped to give a low profile which facilitates insertion of the balloon of the catheter through a blood vessel constriction, however, rewrapping is not easily accomplished after inflation in the body so that the second deflated balloon profile is usually less compact. The wings typically extend diametrically at a distance substantially larger than the diameter of the catheter. The wings may then interfere with a smooth withdrawal of the catheter and even become caught in blood vessels. The force required for a catheter with its balloon in its second deflated profile to recross a treated lesion is therefore typically greater than the force required to initially cross the lesion with the balloon in its initial wrapped profile.
Other problems exist with common balloon materials. For instance, oriented PET balloons formed by stretch blow molding can exhibit pin holes that emit a high-velocity jet of inflation fluid during inflation. This jet may cause artery dissection. PET also exhibits low tear resistance. Because of their thin walls, the balloons are very susceptible to damage, and must be handled with extreme care. PET also will not take a crease, which would be advantageous to facilitate wrapping the balloon.
Smith, U.S. Pat. No. 5,087,246, issued Feb. 11, 1992, describes a balloon dilatation catheter with a fluted balloon having three wings. The balloon in the Smith patent requires that a wire attached to a metal band near the proximal end of the balloon and secured to the balloon at the distal end of the balloon impart a tension to the balloon that will insure that the balloon will assume the fluted configuration when deflated.
It has also been reported in U.S. Pat. Nos. 4,403,612 4,338,942 and 4,608,984,that the problem of rewrapping inelastic catheter balloons can be addressed with dual balloon constructions in which an outer, smaller, balloon of a highly elastic material such as latex, encloses the inelastic dilatating balloon element. 0n deflation the elastic balloon is used to compress the dilatation balloon.
A different type of double balloon construction is employed in copending application Ser. No. 07/927,062, filed Aug. 6, 1992 to provide a dilatation element with non-linear compliance characteristics.
A dilatation balloon is disclosed in EP 420,488 which employs two different concentrically co-extruded polymers to produce a dual layer balloon. An optional lubricity enhancing hydrophilic coating is also mentioned.
It is also known to apply a silicone fluid to the exterior of a dilatation balloon to increase lubricity.
There remains a need in the art to provide improved methods of reducing the profile of deflated dilatation balloons after use, especially non-compliant balloons of inelastic materials such as oriented PET.